The present invention relates to a fluid conduit, a detection system comprising a fluid conduit, and a fluid separation system comprising the detection system.
For detecting optical properties of a fluid, a beam of light may be passed through a volume of the fluid, and after it has passed through a certain volume of the fluid, it is determined how the light has been altered during its passage through the volume of fluid. For example, the fluid may comprise light-absorbing moieties that absorb light, and as a consequence, the intensity of the light may be attenuated at certain wavelengths during its passage through the fluid. Alternatively or additionally, the fluid may affect the polarization of light passing through the fluid.
Fluid conduits for use in detection cells are adapted both for conducting a fluid and for guiding light. To provide for detection with high sensitivity, the light has to travel a certain path in the fluid before it is detected.
Fluid conduits known in the art often use an unprotected outer capillary wall, which can be contaminated by dust or chemicals in the surrounding air. In other solutions, the outer surface of the fluid conduit might be protected by special coatings such as BeF2, BeF2-RbF and others (as disclosed e.g. in U.S. Pat. No. 5,570,447) or by Teflon AF polymer. In EP 1229322 A1, a flexible protection tube is formed outside an inner tube to hold shape of the inner tube.
In high performance liquid chromatography (HPLC), a liquid has to be provided usually at a very controlled flow rate (e. g. in the range of microliters to milliliters per minute) and at high pressure (typically 20-100 MPa, 200-1000 bar, and beyond up to currently 200 MPa, 2000 bar) at which compressibility of the liquid becomes noticeable. For liquid separation in an HPLC system, a mobile phase comprising a sample fluid with compounds to be separated is driven through a stationary phase (such as a chromatographic column), thus separating different compounds of the sample fluid which may then be identified.
The mobile phase, for example, a solvent, is pumped under high pressure typically through a column of packing medium, and the sample (e.g. a chemical or biological mixture) to be analyzed is injected into the column. As the sample passes through the column with the liquid, the different compounds, each one having a different affinity for the packing medium, move through the column at different speeds. Those compounds having greater affinity for the packing medium move more slowly through the column than those having less affinity, and this speed differential results in the compounds being separated from one another as they pass through the column.
The mobile phase with the separated compounds exits the column and passes through a detector, which identifies the molecules, for example by spectrophotometric absorbance measurements. A two-dimensional plot of the detector measurements against elution time or volume, known as a chromatogram, may be made, and from the chromatogram the compounds may be identified. For each compound, the chromatogram displays a separate curve or “peak”. Effective separation of the compounds by the column is advantageous because it provides for measurements yielding well defined peaks having sharp maxima inflection points and narrow base widths, allowing excellent resolution and reliable identification of the mixture constituents. Broad peaks, caused by poor column performance, are undesirable as they may allow minor components of the mixture to be masked by major components and go unidentified.